Currently, there is a great deal of interest in developing alternative energy sources. For instance, there is much interest in developing alternatives to conventional internal combustion engines found in most vehicles. One such alternative energy source being investigated is the fuel cell.
Generally speaking, fuel cells are electrochemical devices that, like conventional batteries, convert the chemical energy of a fuel directly into electrical energy. Unlike conventional batteries, however, fuel cells use externally supplied fuel, such as hydrocarbon fuels, to generate the electrical energy.
Many advantages can be attained through the use of fuel cells. For instance, fuel cells operate with high efficiency due to their ability to directly convert chemical energy to electrical energy. By contrast, internal combustion engines convert chemical energy to thermal energy and then to mechanical energy with substantial losses in accordance with the Carnot cycle. Another advantage provided by fuel cells is that, unlike internal combustion engines, fuel cells do not produce harmful pollutants during operation. Furthermore, fuel cells are low maintenance energy sources in that they require no moving parts beyond those used to deliver fuel to the cells. Additionally, unlike batteries, fuel cells do not deplete with use and therefore do not need frequent replacement or recharging. Many other such advantages exist including low noise production, low vibration, low thermal emissions, high reliability, modularity, fuel flexibility, etc.
FIG. 1 illustrates an example of a known fuel cell. In particular, FIG. 1 illustrates a solid oxide fuel cell (SOFC) 100 of the prior art. As indicated in FIG. 1, the fuel cell 100 generally comprises a first interconnect layer 102, an anode 104, an electrolyte layer 106, a cathode 108, and a second interconnect layer 110. As is apparent from the figure, these various layers are stacked atop one another to form a stacked arrangement that is conventional in the art.
Each interconnect layer 102 and 110 normally is formed of an electrically conductive material (e.g., metal) and serves as both a gas flow field and a current collector. To provide the flow field functionality, the interconnect layers 102 and 110 typically are provided with channels 114 that permit reactant gas (fuel or oxidant as the case may be) to travel along the fuel cell 100. Typically, both the anode 104 and cathode 108 (i.e., the electrodes) comprises a porous material capable of diffusing reactant gas.
In use, fuel is delivered along the channels 114 of the first interconnect layer 102 (indicated by arrow “F”) and oxidant is delivered along the channels 114 of the second interconnect layer 110 (indicated by arrow “O”) so as to create a cross flow of reactant gas within the fuel cell 100. As the fuel travels along its channels 114, the fuel is broken down by the anode 104 into its constituent elements. Simultaneously, the oxidant is broken down by the cathode 108 to form oxygen ions. The oxygen ions are conducted through the electrolyte layer 106 and anode 104 so as to mix with the fuel and, thereby, provide electrons to the fuel. This addition of electrons causes a reaction to occur that generates inert reaction products such as water and carbon dioxide. Through this reaction, an electrochemical potential is created which can be used to generate a current flow, i, from the first interconnect layer 102 when a load (e.g., electric motor) is applied to the fuel cell 100.
Where increased voltage is required, multiple repeatable units 116 can be stacked on top of each other to multiply the voltage output. In such an instance, the second interconnect layer 110 may have a bipolar arrangement that includes a second set of channels 114 that are orthogonally transverse to the first. With such an arrangement, the stack can be continued with a further anode 118 and the other remaining layers of a further repeatable unit 116.
In view of the many advantages of fuel cells such a that shown in FIG. 1, it can be readily appreciated that fuel cells are an attractive option for powering many different types of vehicles, machinery, and equipment. Unfortunately, however, current fuel cell designs are very costly to produce. Specifically, each of the aforementioned layers must be separately fabricated. Where the interconnect layers are to have channels as identified above, the complexity of this fabrication increases, requiring intricate casting or very precise machining. Furthermore, once each of the layers is fabricated, they must be connected (e.g., bonded) to each other with great care. This manufacturing process accounts for approximately 95% of the cost current fuel cells.
Due to the high costs associated with manufacturing fuel cells, their use is not practical. Generally speaking, current fuel cell designs have costs of approximately two orders of magnitude greater than that which would be viable for use in most real-world applications. In view of the many advantages fuel cells provide, it can be appreciated that it would be desirable to a means for manufacturing fuel cells lower costs.